Cytochrome c has long been studied as a protein involved in the electron transport system, and then as an apoptosis-related protein in recent years, and methods for immunochemically measuring intracellular cytochrome c concentrations or blood cytochrome c concentrations are known (Non-patent document 1). Further, since the blood cytochrome c concentration is known to serve as an index of apoptosis occurring in the body (Non-patent document 2 and Patent documents 1 and 2), use thereof as a diagnostic agent for many diseases is being expected.
It has been confirmed that when cytochrome c in a body fluid, in particular, blood, is measured by using conventional cytochrome c measurement methods and measurement kits, measured values reflect amounts of cytochrome c, and there is no problem in investigation of apoptosis occurring in the body. However, so far, whether the measured values accurately reflect the amounts of cytochrome c in body fluids has not been verified, and a measurement method and measurement kit for obtaining an accurate measured value of cytochrome c in a body fluid have been desired.    Patent document 1: WO01/35093    Patent document 2: Japanese Patent Laid-open (Kokai) No. 2003-028860    Non-patent document 1: Andrea Renz, et al., Rapid extracellular release of cytochrome c is specific for apoptosis and markers cell death in vivo, BLOOD, 98(5) 1542-1548, 2001    Non-patent document 2: Z. BEN-ARI, et al., Circulating soluble cytochrome c in liver disease as marker of apoptosis, Journal of Internal Medicine, 254, 168-175, 2003